Solvent-based techniques usually involve preparing dilute blends of
electron-donor and electron-acceptor materials dissolved in a volatile solvent.
After some form of coating onto a substrate, the solvent evaporates. An
initially homogeneous mixture separates into electron-acceptor rich and
electron-donor rich regions as the solvent evaporates. Depending on the
specifics of the blend and processing conditions different morphologies are
typically formed. Experimental evidence consistently confirms that the
morphology critically affects device performance. A computational framework
that can predict morphology evolution can significantly augment experimental
analysis. Such a framework will also allow high throughput analysis of the
large phase space of processing parameters, thus yielding insight into the
process-structure-property relationships.
In this paper, we formulate a computational framework to predict evolution of
morphology during solvent-based fabrication of organic thin films. This is
accomplished by developing a phase field-based model of evaporation-induced and
substrate-induced phase-separation in ternary systems. This formulation allows
all the important physical phenomena affecting morphology evolution during
fabrication to be naturally incorporated. We discuss the various numerical and
computational challenges associated with a three dimensional, finite-element
based, massively parallel implementation of this framework. This formulation
allows, for the first time, to model 3D morphology evolution over large time
spans on device scale domains. We illustrate this framework by investigating
and quantifying the effect of various process and system variables on
morphology evolution. We explore ways to control the morphology evolution by
investigating different evaporation rates, blend ratios and interaction
parameters between components
